1. Catapult Launches and Eco-Climbs The only reason that aircraft need giant engines is for getting off the ground in the first place. Once they reach cruising altitude, all that power (and weight) is a waste. Airbus is thinking about ways to offload some of that take-off power requirement from the aircraft itself, and one way to do that is with some sort of ground-based catapult system like you'd find on an aircraft carrier. It would be a fun experience for passengers, with an aggressive launch and steep climb, and beyond 2050, Airbus is even thinking about a similar system for landings, which would eliminate the need for landing gear.

2. Flying in Formation Currently, antiquated air traffic control systems prevent aircraft from flying along the most efficient routes to their destinations, making every flight 10 to 20 minutes longer than necessary, which adds up to over 500kg of wasted fuel and 2,000kg of extra CO2 emissions per flight. Upgraded instruments should allow aircraft to fly along direct routes, and also much closer together, "surfing" on each other's turbulence like birds do. Flying in a "V" formation would reduce drag by 65%, leading to 10% fuel savings and a reduction of emissions of up to 25%.

3. Smarter Approach and Landings Landing a commercial aircraft at a busy airport generally involves flying in circles in a holding pattern while waiting for a landing spot to open up. This wastes time and fuel, and means that aircraft are landing at much higher speeds than they would be otherwise, since they can't optimize their descent. New technology that optimizes landing positions would take care of this, enabling aircraft to make gradual efficient descents, saving time and fuel and reducing required runway length by 1/3. As aircraft touch down, their kinetic energy would be captured and used to power on-board systems.

4. Low Emission Ground Operations Airplanes are for flying, not for driving, and anything that they do on the ground is horrendously inefficient. With autonomous renewably-powered taxiing robots, aircraft could be met at the end of the runway and towed to their gates without having to use their engines at all. This could potentially save six million tons of CO2 per year.

5. New Fuels There's no way around the fact that aircraft, in order to do that flying thing, have to burn fuel, and burning fuel is bad for the environment. Airbus has been experimenting with mixing conventional jet fuel with renewable biofuels, which would reduce CO2 emissions by between 50% and 80%. Looking even farther into the future, Airbus envisions aircraft that are powered by fuel cells, and powering on-board systems by harvesting body heat directly from passengers.